1. Field of the Invention
The present invention relates to a method for producing a homopolymer or copolymer of an .alpha.-olefin. More particularly, the present invention is concerned with a method for producing a homopolymer or copolymer of an .alpha.-olefin in which a specific catalyst is used, said catalyst comprising a solid catalyst component obtained by contacting, in the presence of a chlorinated hydrocarbon solvent, a titanium compound and an aromatic carboxylic ester with a solid component obtained by reacting a hydrocarbon solvent-soluble organomagnesium compound having an alkoxy group with a specified chlorosilane compound having an Si--H bond; and organoaluminum compound; and an alkoxysilane compound. By the method of the present invention, an .alpha.-olefin homopolymer or copolymer exhibiting high bulk density and stereoregularity can be efficiently produced even under such polymerization reaction conditions, such that the polymerization temperature is high and the polymerization time is long.
2. Discussion of Related Art
It is well known in the art that a catalyst system comprising a titanium halide and an organoaluminum compound, such as triethylaluminum and diethylaluminum chloride, is useful for commercial production of an .alpha.-olefin polymer having high stereoregularity.
Further, various catalyst systems comprising a solid component composed of magnesium chloride, a titanium halide and a carboxylic ester, triethylaluminum and an electron donor, have heretofore been proposed as highly active catalyst systems which are useful for commercial production of an .alpha.-olefin polymer having high stereoregularity. For example, it was proposed in U.S. Pat. No. 4,156,063 to use a catalyst system comprising a solid catalyst component composed of activated MgCl.sub.2, a titanium halide and a carboxylic ester; an organoaluminum compound; and a carboxylic ester. However, the polymerization catalytic activity of this catalyst system per unit weight thereof is not sufficiently high so as to be commercially useful, and also the polymer obtained using this catalyst system does not have a satisfactorily high stereoregularity.
As disclosed in U.S. Pat. No. 4,159,256, the present inventors previously found that a polymer having high stereoregularity is obtained in high yields by the use of a catalyst system comprising a solid catalyst component obtained by reacting a titanium halide and a carboxylic ester with an alkyl group-containing magnesium halide obtained by reacting an organomagnesium component with a chlorosilane compound having a Si--H bond; a carboxylic ester; and an organoaluminum compound.
Moreover, as disclosed in Japanese Patent Application Publication Specification No. 60-11924, the present inventors found that, with respect to a catalyst system comprising the above-mentioned solid catalyst component, an alkoxysilane and an organoaluminum compound, the degree of lowering of the catalytic activity with time is advantageously small.
On the other hand, in EP-A-45,977, it is described therein that when a catalyst system comprising the above-mentioned type of solid catalyst component containing a specific carboxylic ester, such as a phthalic diester, an alkoxysilane and an organoaluminum compound is used, the catalyst system exhibits markedly increased activity, and by the use of this catalyst system, a final polymer having markedly enhanced stereoregularity can be obtained. In the specification of EP-A-45,977, use is described of, for example, a solid catalyst component prepared by introducing anhydrous magnesium chloride, an aromatic carboxylic diester and titanium tetrachloride into a ball mill apparatus, in which the feedstock components are pulverized for a prolonged period of time, and then suspending the resultant pulverized mixture in 1,2-dichloroethane, followed by heating.
Furthermore, in EP-A-156,512, it is described that when a solid catalyst component prepared by effecting a reaction of a hydrocarbon-soluble dialkoxymagnesium not containing any alkyl group, an electron donor and hydrochlorosilane to obtain a solid component and subjecting the obtained solid component to a reaction with a titanium compound is used, a polymer having high bulk density and stereoregularity can be produced in high yields.
While the above-mentioned conventional catalyst systems have a high catalytic activity for producing a homopolymer or copolymer of an .alpha.-olefin which has relatively high stereoregularity, these systems have inherent problems which limit their applications. For example, when the above-mentioned conventional catalyst systems are applied to a liquid polymerization or gas phase polymerization of propylene (at temperatures of 75 .degree. C. or higher), the polymerization catalytic activities of the catalyst systems are not satisfactorily high, and the stereoregularity and bulk density of the final polymer are also not satisfactorily high. Further, when a block copolymerization of propylene with another monomer is performed using the above-mentioned conventional catalyst systems, it is likely that the formed copolymer particles will be sticky which would cause the agitation of the reaction mixture to become difficult and hence the block copolymerization cannot be continued.